Flow numbers and max HP potential

I saw a video choosing a cam that claimed (in a general sense) if you take the flow of an intake port for a given lift, and multiply it by 0.26, that will give you the max theoretical hp for that cyl at that lift. So for magnum heads, that's 233 from the factory as far as I understand, so at that rate, each cyl should be able to support 60.5 HP, or a total of 484 HP. How far off of reality us that? I understand reality over theoretical but software can effectively predict HP based on such things so how far off is this?

Opinions?
Link to the video?
I would like to view it.